As digitization of information proceeds, techniques for obtaining desired images by digital signal processing on input images have been proposed. In capturing an image of an object using an image pickup apparatus, considerable degradation is caused to an obtained image by aberration occurring in an image pickup optical system. One known technique for correcting degradation in image is correction using information on an optical transfer function (hereinafter referred to as OTF) of an image pickup optical system.
Japanese Patent Laid-Open No. 2007-183842 discloses an image restoration filter as which an optical transfer function (OTF) obtained by Fourier transform of a point spread function describing degradation in image caused by an image pickup optical system is used. The image restoration filter is capable of continuously adjusting the degree of image restoration of a captured image by allowing its parameter to be adjusted.
However, even when image restoration is performed using an image restoration filter in Japanese Patent Laid-Open No. 2007-183842, if aberration for each color component caused by an image pickup optical system differs from expected aberration characteristics, unexpected chromatic blurring occurs in the captured image and its image quality degrades.
Such chromatic blurring can be caused by variations in image pickup optical systems resulting from manufacturing errors, spectral changes under image capturing environment, image capture of a three-dimensional object, or luminance saturation. Image pickup of a three-dimensional object is described below as one example of a situation where chromatic blurring occurs. An image pickup apparatus focuses on one plane in an object space by the autofocus function or manual focusing to capture an image. When the object is a three-dimensional object, its object distance varies with an angle of view. In this case, if the object is in focus, its image is relatively sharply captured, whereas if the object is out of focus, blurring according to its distance occurs in its image. When traditional image restoration processing is preformed on a captured image having such a blur, if the object is in focus, desired sharpness is obtainable for its edges because the image restoration filter is optimal. However, if the object is out of focus, chromatic blurring may occur in the edges or chromatic blurring may be large unnaturally. The occurrence of such chromatic blurring in image restoration processing for improving the image quality of an output image significantly degrades the image quality.
Accordingly, it is an object of the present invention to provide an image processing apparatus capable of reducing the occurrence of unnatural chromatic blurring that can occur in traditional image restoration processing and capable of obtaining good image quality.